The present invention relates to a fluid control valve used for hydraulic actuating systems. More specifically, it relates to a fluid control valve which can be used for multi-purposed control of large volume main flows by utilizing pilot flows of a small volume.
Although the method of controlling main flows of large volume by using their small volume pilot flows is generally used in hydraulic actuating systems, no single fluid control valve applicable for various control purposes is yet available. According to each case, therefore, several fluid control valves each having a specific purpose and construction must be employed in combination to form an appropriate circuit module. In order to meet each circuit requirement, various fluid control valves having various functions are required. Such a lack in versatility of fluid control valves makes their standardization difficult, and is also disadvantageous for production control.
In view of above, we have already presented a unique fluid control valve which may resolve the said defect in our Application No. 319306 filed Dec. 29, 1972 (No. 60058 in the United Kingdom, No. 160264 in Canada and No. P2264091.1 in F.R. Germany). In the said invention, however, even though the fluid control valve for a pump section may be provided with a load, no-load function or with a main relief function by installing an on-off valve or a main relief valve in its pilot circuit, it has not been possible to provide a load-check function which is necessary in most cases involving fluid control valves of this kind for pump section use. In cases where the load-check function is required, therefore, a load-check valve must be installed in the circuit. Thus, it is desirable for every fluid control valve used in the pump section to perform the load-check function also.
In addition, although the fluid control valve we have presented before is very versatile as compared with conventional ones, fluid control valves differing in valve body construction, and complex circuit compositions are required in some cases, depending on whether the valve is used in the pump section or the cylinder section, whether a carryover function is required or not, and whether special circuits such as a quick-feed circuit or a high-low speed switchover circuit are involved or not. If a single fluid control valve applicable for all these various uses without change in its valve body construction is developed, it should produce a tremendous effect on production control due to its increased versatility.